1. Field of the Invention
The present invention relates to a semiconductor integrated circuit, and specifically to a semiconductor integrated circuit having a function selecting circuit for selecting a prescribed function circuit by bonding option.
2. Description of the Related Art
A technology referred to as bonding option is known as a method for selecting a desired function circuit among function circuits included in semiconductor integrated circuits. According to this technology, the wiring from lead frames of a semiconductor integrated circuit to power supply pads is changed to select a desired function circuit among a plurality of function circuits having different functions. Using bonding option during the production of semiconductor integrated circuits, a prescribed function circuit can be selected without changing a mask for wiring after impurity diffusion is finished. In this way, semiconductor integrated circuits having different functions can be produced without changing any production integrated circuit can be reduced.
According to general bonding option, one power supply pad connected to a prescribed circuit to be selected and a specific lead frame terminal connected to a prescribed potential outside the chip package are connected to each other by a bonding wire. By thus connecting the power supply pad, the function circuit connected to the power supply pad is made effective. By connecting the power supply pad to a grounded lead frame, the function circuit connected to the power supply pad is made ineffective.
With bonding option, the power supply pad corresponding to the selected function circuit is connected to a bonding wire for supplying power to the selected function circuit, and power supply pads corresponding to unselected function circuits are not connected to any bonding wires. Accordingly, the potential of each of the power supply pads corresponding to the unselected function circuits fluctuates. When this occurs, the unselected function circuits which should not operate may undesirably malfunction. Such a malfunction tends to occur more easily as the integration degree of semiconductor integrated circuits is improved.
Therefore, the power supply pads of unselected function circuits need to be grounded so that the potential of the power supply pads is fixed.
Japanese Patent No. 2054176 discloses a semiconductor integrated circuit in which power supply pads respectively corresponding to function circuits are grounded via resistors. According to the technology disclosed in Japanese Patent No. 2054176, the potential of the power supply pads corresponding to the unselected function circuits is fixed to the ground level and thus does not fluctuate.
The semiconductor integrated circuit described in Japanese Patent No. 2054176, however, has the following drawback. The power supply pads respectively corresponding the function circuits are grounded via resistors, as described above. Accordingly, when a bonding wire is connected to an power supply pad of a selected function circuit so as to fix that power supply pad to an operating potential of the selected function circuit, a shoot-through current flows to ground from the power supply pad via the resistor. When the shoot-through current flows, power consumption of the semiconductor integrated circuit is undesirably raised.
According to one aspect of the invention, a semiconductor integrated circuit includes a plurality of units. Each of the units includes a power supply pad, a function circuit, and a power supply control circuit. The plurality of units each have a first state in which the function circuit is in an operating state by the power supply pad being at a prescribed operating potential and a second state in which the function circuit is in a non-operating state by the power supply pad being at a prescribed non-operating potential. The power supply control circuit includes a switching circuit for connecting the power supply pad to the prescribed non-operating potential. The power supply control circuit in each of the plurality of units closes the switching circuit when at least one of the other units is in the first state and opens the switching circuit
In one embodiment of the invention, the semiconductor integrated circuit further includes a resistor connected to the switching circuit in series.
In one embodiment of the invention, the semiconductor integrated circuit further includes a signal control circuit for selectively outputting an output from one of the function circuits based on potentials of the power supply pads in the plurality of units.
In one embodiment of the invention, the power supply pad in one of the plurality of units is connected to a terminal having the prescribed operating potential via a conductive member.
In one embodiment of the invention, the conductive member is a bonding wire.
In one embodiment of the invention, the terminal includes a plurality of first terminal regions, the power supply pad includes a plurality of second terminal regions, and the conductive member is applied or caused to adhere by pressure to the plurality of first terminal regions and the plurality of second terminal regions.
Thus, the invention described herein makes possible the advantages of providing a semiconductor integrated circuit having a function selecting circuit operable at a high level of reliability while consuming low power.